Physiologically active peptides such as growth factors are administered to birds in ovo to achieve a physiological effect in the birds. For example, U.S. Pat. No. 5,028,421 to Fredericksen discloses a method for increasing the weight of treated birds after hatch by introducing a T-cell growth factor into eggs on about the eighteenth day of incubation.
Current literature suggests both insulin and insulin-like growth factors are physiological regulators of embryonic growth and differentiation. Both insulin and IGF-1 affect metabolism and growth, and a variety of cells differentiate in vitro when exposed to these growth factors. See, e.g., Girbau et al., Endocrinology 121, 1478 (1987).
Chicken IGF-1 has been chemically purified and characterized. Some evidence correlates growth rate and endogenous circulating IGF concentrations in poultry. See, e,g., Scanes et al., Growth Dev. Aging 53, 151-157 (1989).
Due to the lack of availability of native or synthesized chicken IGF-1, experimental studies of the biological effects of IGF-1 in poultry have used human IGF-1. Human IGF-1 in vitro has been shown to specifically influence the metabolism, differentiation, and proliferation of cells from embryonic and posthatch chicks in vitro. See, e,g., Vasilatos-Younken and Scanes, Poultry Science 70, 1775 (1991).
In ovo administration of human IGF-1 to poultry has been studied previously. The effect of human IGF-1 administered into the allantois of day 7 and day 14 chick embryos was reported by Spencer et al., Reprod. Nutr. Dev. 30, 515-521 (1990). The posthatch data of Spencer et al. indicated that there were no significant differences between treated and control groups in weight gain or several other measures of growth. The reference concludes that the administration of exogenous IGF-1 from day 7 to day 14 does not stimulate growth in the chick embryo.
Girbau et al., Endocrinology 121, 1477-1482 (1987), disclose the administration of recombinant human IGF-1 to 2 day old chick embryos by injection (injection site not disclosed). The embryos were sacrificed at day 4, and various biochemical indices were compared to non-injected controls. Extracts of day 4 embryos showed accelerated development, although even greater acceleration in development was seen in embryos injected with insulin. Girbau et al. report that they believe "[t]he stereotype which considers insulin a metabolic hormone and IGF-1 a growth hormone is far too restrictive," and "that insulin and IGF-1 may have a regulatory, complementary, or overlapping role in normal chick embryo early development" which suggests a belief that administration of IGF-1 alone is not a method of enhancing growth.